Molecular dynamics study of fission gas behaviour and solubility in molten FLiNaK salt

Abstract

The solubility of fission products in molten salts is an important factor in predicting their rate of release, and their buildup can affect the salts’ performance. In this work, a molecular dynamics study of dissolved Ar, Xe, Cs+ and I− in molten FLiNaK is undertaken. The work includes a method for the determination of the interatomic potential parameters based on DFT calculations and tuned such that experimentally determined densities are achieved. Simulations were used to estimate diffusion coefficients for each solute. Additionally, the effects of dissolved CsI on the thermophysical properties, such as heat capacity, viscosity and thermal conductivity of the salt, are also predicted. Alchemical free energy calculations are used to determine the solutes’ solvation free energies, and trends due to changes in concentration and temperature are examined and compared favourably to experimental results found in the literature. Thus, it was found that molecular dynamics simulations can be used to predict the behaviour of solutes in molten salts, and the effects of their presence on the properties of the salt.